“Slide-ring gels”, new gels different from physical gels and chemical gels, have been developed in recent years. A compound that is used for such slide-ring gels and draws attention is a crosslinked polyrotaxane.
A crosslinked polyrotaxane has a structure in which linear molecules thread through cyclic molecules in a skewered manner and the cyclic molecules are movable along the linear molecules (a pulley effect). The pulley effect allows the crosslinked polyrotaxane to be viscoelastic and to uniformly distribute tensile force applied thereto. The crosslinked polyrotaxane is therefore not likely to have cracks or flaws, i.e., has excellent characteristics that conventional crosslinked polymers do not have. Such a crosslinked polyrotaxane is obtainable by placing a capping group at each end of a linear molecule of pseudopolyrotaxanes to prevent dissociation of the cyclic molecules of pseudopolyrotaxanes and crosslinking the resulting polyrotaxanes. The pseudopolyrotaxanes have a linear molecule which is included in the cavities of the cyclic molecules in a skewered manner.
The pseudopolyrotaxane used for production of a crosslinked polyrotaxane arises from mixing of a polyethylene glycol and a cyclodextrin in an aqueous medium, in general. Thus, the pseudopolyrotaxane is produced in a state of aqueous dispersion.
Patent Literature 1 discloses that a white gelatinous aqueous dispersion of pseudopolyrotaxane is obtainable by dissolving amino group-terminated polyethylene glycol with an average molecular weight of 2,000 and α-cyclodextrin in distilled water, then stirring the mixture for one hour at 80° C. to yield a transparent solution, and cooling the obtained transparent solution in a refrigerator (5° C.) overnight.
Patent Literature 2 discloses that a white paste-like aqueous dispersion of pseudopolyrotaxane is obtainable by dissolving polyethylene glycol bis(amine) with a number average molecular weight of 20,000 and α-cyclodextrin in water under heating up to 80° C., then cooling the obtained solution, and leaving the solution to stand at 5° C. for 16 hours.
Patent Literature 3 discloses that a cream-like aqueous dispersion of pseudopolyrotaxane is obtainable by dissolving carboxyl group-terminated polyethylene glycol and α-cyclodextrin in separately prepared warm water (70° C.), then blending the solutions, and leaving the mixture to stand in a refrigerator (4° C.) overnight.